Method for continuously drying bulk goods, in particular wood fibers and/or wood chips

ABSTRACT

The invention proposes a method for drying bulk goods, in particular wood fibers and/or wood chips, wherein the bulk goods is continuously dried in a dryer ( 1 ), in particular a drum dryer. The vapor-gas mixture flows through the drum dryer ( 1 ) in a dryer circuit and is indirectly heated via at least one heat exchanger ( 4 ) by a burner waste gas that is heated in at least one burner ( 5 ). The drying vapors are supplied to the at least one heat exchanger ( 4 ). Upstream, downstream and/or within the at least one heat exchanger ( 4 ), at least a partial flow of the drying vapors are branched off to be conducted into the burner ( 5 ). The remaining partial flow is conducted to the dryer ( 1 ) again. The partial flow of drying vapors to the burner ( 5 ) is driven by means of at least one regulable partial vapor fan ( 10 ).

The present invention relates to a method for continuously drying ofbulk goods, in particular wood fibers and/or wood chips, in a dryer,wherein the drying vapors are led to a dryer circuit, in which thedrying vapors are indirectly heated via a heat-exchanger and areconducted to the dryer again.

The manufacturing of boards made from wood materials is basedessentially on the pressing of hackled wood pieces, in particular ofwood fibers and/or wood chips. For example, a chip board consists ofsmall wood chips with different thickness, which are pressed togetherwith a binder and under application of high pressure to form boards.Wood fiber boards are produced from wooden fiber with or without anadditional bonding agent.

Before being pressed to boards, the hackled wood pieces have to bedried. This is usually done in so called drum dryers, wherein the goodsto be dried respectively the bulk goods are moved in a heated, rotatingtube. During the drying also gaseous wood contents are freed in additionto water vapor, which must not be released to the environment since theyare considered as pollutants. The drying vapors are further contaminatedwith fine particulate matter. For this reasons, the drying vapors haveto be cleaned before they can be released to the environment. This isachieved usually by dust removal, filtering and/or a burn-out in theburner of the dryer. To reduce the costs for this treatment of thedrying gases and in particular to reduce the additionally necessaryenergy consumption, different methods and apparatuses are suggested,which enable a more economic process by guiding the drying gases in acircuit and subjecting the same to an indirect heating via a burner.

The European patent application EP 0 459 603 A1 describes for example adrying of wood fibers in a drum dryer, wherein the drying vaporsexciting the dryer are led back in a circuit to the dryer and are heatedindirectly through the heating gas produced by the burner until theyreach the temperatures necessary for drying the wood chips. A part ofthe drying vapor is removed from this circuit and guided to thecombustion chamber. The exhaust gases from the combustion chamber, whichare used to heat-up the drying gases via a heat-exchanger, are cleanedwith a filter, before they are released to the environment.

The European patent application EP 0 457 203 A1 describes also a dryingmethod among others for wood chips, wherein the drying gases areindirectly heated by a heat-exchanger and wherein the heat-exchanger isenergized with the exhaust gases of a combustion chamber. A part of thedrying vapors is continuously removed from the dryer and fed to acondenser wherein the water contend is condensed and wherein thenon-condensable gases are led as combustion air into the combustionchamber.

With these methods the temperatures in the combustion chamber have to bekept sufficiently high, to assure the burning off of any pollutants.These high temperatures put a strain to the elements of theheat-exchanger so that the lifetime thereof is reduced. For this reason,the European patent application EP 0 714 006 suggests a drying method,wherein a second heat-exchanger is arranged before the firstheat-exchanger in order to reduce the thermal strain of the material.

During the drying process in the circuit constantly new vapors areproduced which are contaminated with pollutants. The circulating dryingvapors therefore have to be continuously removed, to achieve a massbalance. This is done for example by removing a part of the dryingvapors downstream or upstream of the heat-exchanger and to guide thispart as combustion air to the burning chamber. For the control of theflow rate the European patent application EP 0 714 006 A1 suggests forexample a valve.

A problem of the known methods is, that the system may not reactsufficiently to changing conditions as for example to changing moisturecontent, changing grain size, changes in the wood mixture or changes inthe load. It is therefore the object of the present invention to providean improved method for the continuous drying of bulk goods, which avoidsthe mentioned disadvantages from the prior art.

This object is solved by a method and an apparatus, as it is describedin the independent claims. Preferred embodiments of the inventive methodrespectively the inventive apparatus are described in the sub-claims.

With the inventive method for continuously drying of bulk goods, inparticular wood fibers and/or wood chips in a dryer in particular a drumdryer, the dryer is fed with the bulk goods, and a vapor gas mixture isguided there through in a drying circuit. Hereby the vapor gas mixtureis indirectly heated via at least one heat-exchanger with burner exhaustgases from a burner. After passing through the dryer, the drying vaporsare guided to the at least one heat-exchanger and are heated-up again.Upstream, downstream and/or within the at least one heat-exchanger, atleast a partial flow of the drying vapors is branched off to be guidedas cooling air and/or as combustion air to the burner. The remainingpartial flow is again guided to the dryer, after it was heated-up in theat least one heat exchanger. Preferably, two parallel arrangedheat-exchangers are used, which are operated in cross counter flow.Particularly advantageously, a part of the drying vapors is branched offwithin the heat-exchanger since a branching off within the heatexchanger provides energetic and emission advantages.

In view of the actual drying method the vapor circuit drying achieves agentle drying and a oxygen reduced atmosphere with a reduced amount ofremoved polluting compounds and thus a quality improvement of the dryinggoods compared to other drying methods. It allows to increase theflexibility and the softness of the wood chips, which is in particularadvantageous in view of the later processing of the wood chips and thequality of the end product. By means of the vapor circuit for thedrying, which is achieved by the indirect, essentially oxygen freeheating of the drying gases via a heat-exchanger, an inert gas contentis achieved, which effects as a further advantage a reduced wear of theapparatus and an increased security due to a reduced risk of fire andexplosions.

The inventive method is characterized by the fact, that the partial flowof the drying vapors which is removed upstream, downstream and/or withinthe heat exchanger to the burner, is driven by a regulable partial vaporfan.

The inventive regulable partial vapor fan allows a controlled burningoff of pollutants in the burner of the drying arrangement. Due to theregulable partial vapor fan, the flow rate and flow speed of the partialflow of the drying vapors to the burner can be adjusted to therespective conditions of the drying process. It is for example possibleto react to certain properties of the drying goods, as for examplemoisture content or mass flow, by removing for example a larger partialflow of the drying vapors to the burner if an increased moisture contentis recognized. This secures an optimal process control and an effectiveremoval of pollutants by a burn-out in the burner. The regulable partialvapor fan allows that the mass respectively volume flows can beincreased and that thereby the output of the drying process cansignificantly be increased. The oxygen content in the dryer can becontrolled to a minimum to minimize the production of organic compoundsand to reduce thereby the emissions. Additionally, due to the regulablepartial vapor fan the burn-out performance as well as the distributionof the vapors in the burning chamber can be influenced whereby theemissions can be further reduced.

Advantageously, upon regulating the partial vapor fan, the mass balancein the system is considered, so that for example the introduction ofleak air into the system can be reduced. The uncontrolled intrusion ofleak air into the system leads to energetic disadvantages, since theleak air has to be heated-up in the system before it can be used in theprocess. The control therefore keeps the amount of leak air in a certaincorridor.

In a particularly preferred embodiment of the inventive method, thecontrol of the partial vapor fan is carried out taking into account thelevel of pollutants in the exhaust gases of the burner. The level ofpollution may for example be directly measured before the exhaust gasesof the burner are released to the environment, wherein the exhaust gasesof the burner are preferably cleaned beforehand. As levels of pollutantspreferably the concentration of nitrogen oxide and/or the concentrationof carbon monoxide of the exhaust gases of the burner can be considered.According to the invention it can be provided, that certain thresholdsof these concentrations are determined and that the regulable partialvapor fan is effected if these pollution thresholds are not met.Further, according to the invention it may be provided that a control ofthe regulable partial vapor fan is carried out considering the oxygencontent in the exhaust gas of the burner. Depending on the fuel used forexample the control may be carried out according to an oxygen content ofapproximately 3 Vol % up to approximately 11 Vol % in the exhaust gas.

In a further preferred embodiment of the inventive method, the controlof the regulable partial vapor fan is carried out taking into accountthe maximum inert gas content in the drying circuit, preferably bymeasuring the oxygen content and/or the water content in the dryingvapors. Thereby an increased output of the drying method as well as anincreased quality of the drying goods, for example an improved qualityof the wood chips, can be achieved. By maximizing the inert gas contentin the drying circuit the deposition, pollution and thus the wear ofdifferent parts of the apparatus are kept to a minimum. Additionally,the security of the apparatus is increased due to the minimization ofthe risk of fire and explosion.

In a preferred embodiment of the inventive method the exhaust gases ofthe burner, which are removed from the system, are passed to a filter,in particular an electrostatic precipitator preferably a dry typeelectrostatic precipitator for cleaning therefore. A filtering of theexhaust gases of the burner is in particular advantageous in the case ofwood dust being burned in the burning chamber to reduce the emissions.An electrostatic precipitator has the advantage that compared toordinary bag filters the risk of fire is reduced. A dry typeelectrostatic precipitator has shown to be particularly effective incleaning the exhaust gases of the burner. It is particularly preferredto operate the filter, in particular the electrostatic precipitator, ina suction operation, wherein preferably downstream of the filter aburner exhaust gas fan is arranged. The suction operation isadvantageous, since the under pressure deriving there from offersadvantages with regard to the construction of the filter and since thefan is protected from wear. As fuel for the burner ordinary fossil fuelsmay be used as for example natural gas or oil. In a particularlypreferred embodiment additionally or alternatively solids are used inparticular biomass. For example, waist from the production of the woodenboards, as for example wood dust or similar, may be burned. Theadvantage of this process is, that waste, which is produced anyway, canbe used as fuel in the combustion chamber.

In a preferred embodiment of the inventive method a cleaning device isprovided for the drying vapors, which vapors contain in particular finedusts and different organic parts deriving from the drying of the bulkgoods. As cleaning device, one can for example use a cyclone separator,in particular one or more cyclone batteries. Inside of the cyclone thesolid or liquid particles, as for example fine dusts, contained in thedrying gases are separated, by transferring the drying gases into arotary motion, whereby the centrifugal force acting on the particleswill accelerate the particles and move them radically outwardly.Thereby, the particles can be separated from the gas and may preferablybe removed downwards. Between the dryer and the cleaning device, as forexample the cyclone batteries, and/or between the cleaning device andthe heat-exchanger the drying vapors are preferably driven by means of adrying vapor fan. Due to the flow circuit of the drying gases the dryingvapor fan is protected from dirt and thus wear.

In a particularly preferred embodiment of the inventive method the watercontent in the dryer is controlled. The bulk goods, as for example thewood fibers or wood chips, are advantageously separated to differentfractions depending on the moisture contend and the bulk goods aremetered from the different fractions via a metering device, such that adesired moisture content can be maintained in the bulk goods introducedto the dryer. For example, three silos each containing a certain fibertype may be provided, wherein each fiber type has a particular moisturecontent. The moisture of the bulk goods to be dried, and which are movedto the dryer, can for example be continuously measured. For example bymeans of a detected program the composition of the drying goods can becontrolled, such that a continuous water flow in the dryer can besecured. The control can be achieved in a particular advantageous mannersuch that the water flow in the dryer remains constant. This control ofthe water content in the dryer has the advantage, that differing moistercontents in the drying goods, as for example the wood fibers, can bebalanced out. Further, due to the control of the water content in thedryer, the inert gas content in the drying circuit can be optimizedwhich is for example advantageous in view of the quality of the dryinggoods and increases in addition the output of the drying process.

In a particularly preferred embodiment of the inventive method furtherexhaust gases are fed to the burner as combustion air, as cooling airand/or for muffle cooling. Preferably these further exhaust gases aretaken from the production process of the wood material boards, as forexample exhaust air from the pressing devices, exhaust gases from thesawing devices ect. This integration of different emission sources intothe inventive method has the advantage, that the different exhaust gasescan be post-treated in the combustion chamber, to achieve thereby aburn-out of the pollutants in the exhaust gases. Due to economic reasonsit is preferred to post treat all the different exhaust gases, inparticular all the exhaust gases deriving from the manufacturing of thewood material boards in this way. Preferably, the additional exhaustgases are pre heated before they are supplied as combustion air. To thisaim different heat-exchangers may be provided, as for example thermaloil heat exchanges. By pre heating the exhaust gases before the same areguided to the combustion chamber the necessary temperature in thecombustion chamber can be achieved in a particular economic manner.

In a particularly preferred embodiment of the inventive method thecooling air supply to the burner is achieved via an interior and anexterior nozzle ring in the ceiling of the combustion chamber. It isparticularly preferred, that these nozzle rings can be controlledseparately from each other. Preferably, the inner nozzle ring and/or theouter nozzle ring are provided with a pre-adjusted entering angle forthe respective fuel which is in the range between approximately 0 andapproximately 60 degrees. Due to this construction of the cooling airsupply respectively of the ceiling of the combustion chamber and theparticular air supply in the combustion chamber as well as the guidingof the secondary air and the condensation deriving there from,combustion in the combustion chamber is achieved in a particularadvantageous manner.

The cooling air supply into the burner can for example be taken from thepartial vapor flow, which is for example branched off from theheat-exchanger. The control of the different rings is preferablyachieved with suitable valves.

In a further preferred embodiment of the inventive method, the muffle ofthe burner is cooled. For example, the muffle may be cooled with freshair. In another preferred embodiment the cooling of the muffle is donewith process air. For example, one can use as cooling air for the mufflewhich is branched off from the partial flow of the drying vapors, orfrom partial flows branched off the drying vapors upstream, downstreamand/or from within the heat exchnagers(s). In alternative embodimentsexhaust gases of the burner are used as cooling air, after the same arepassed though the heat-exchanger and/or exhaust gases, which arebranched off before releasing via the chimney and in particular exhaustgases which have been passed through the filter. The control of themuffle cooling is preferably dependent on the temperature of the muffle,to protect the muffle. The control can further be done dependent on thecarbon monooxide content of the exhaust gases, wherein additionally thetemperature control of the muffle can be used.

The invention relates further to a method for the manufacturing ofwooden material boards, wherein wood logs are stripped of bark and areprocessed in a crushing device to fibers and/or wood chips, inparticular in a milling machine. The chips and/or fibers are dried in adrying apparatus and—if necessary by adding binders and/or furtheradditives—processed to boards in a pressing device and if necessary cutto size. This method is characterized in that for the drying of thechips and/or fibers a method is used as it was described above. Withregard to further features of the method for the manufacturing of woodenmaterial boards it is referred to the above description.

The invention further relates to an apparatus for the drying of bulkgoods, in particular of wood fibers and/or wood chips, with a dryer, inparticular a drum dryer, through which a vapor gas mixture is passed ina drying circuit. The apparatus further comprises at least oneheat-exchanger for the indirect heating-up of the vapor gas mixture andit comprises a burner. The burner creates exhaust gases, which can beused for the indirect heating of the vapor gas mixture. Further, atleast one branch line to the burner is provided upstream, downstreamand/or within the at least one heat-exchanger for a partial flow of thedrying vapors and at least one line is provided for the remaining partof the drying vapors to the dryer.

The inventive apparatus is characterized in that at least one regulablepartial vapor fan is provided to move the partial flow of the dryingvapors to the burner. Concerning further features of the inventiveapparatus it is referred to the above descriptions.

Finally the invention relates to an apparatus for the manufacturing ofwooden material boards comprising at least one crushing device, inparticular a milling machine, at least one pressing device and at leastone drying device for bulk goods, as it was described above. With regardto further features of this apparatus for the manufacturing of woodenmaterial boards respectively with regard to the drying device of thisapparatus it is referred to the above description.

The inventive method for drying of bulk goods is in particular suitedfor the drying of wood chips. The inventive vapor atmosphere in thedrying circuit has positive effects to the quality of the wood chips.The gentle drying of the wood chips realized thereby achieves flexibleand soft wood chips, which do not show any thermal discoloration. Due tothe inert gas atmosphere during the drying the ignition potential of thedrying goods and thus the fire hazard in the dryer respectively in thewhole apparatus can be reduced. The same is true, if the inventivemethod is used for the drying of wood fibers. When drying wood fibers itis in particular the inventive controlled and adjusted moister contendin the drying goods which is advantageous, since the moisture of woodfibers is usually very problematic in the sub-sequently followingprocessing of the fibers, in particular in the press section. Differentfrom the processing of wood chips no intermediate storage of the driedwood fibers takes place. Rather, the pressing of the wood fibers followsdirectly after the drying, so that the moisture content of the dryinggoods corresponds directly to the moisture in the press section. Theinventive method has the advantage that a controlled and continuousquality of the dried bulk goods can be provided for the furtherprocessing.

Further advantages and features of the invention derive from thefollowing description of the drawings in connection with the preferredembodiments and the sub-claims. Hereby, the different features may berealized alone or in combination with each other. In the drawings:

FIG. 1 shows a schematic illustration of a process picture for anapparatus, which is suitable for a preferred embodiment of the inventivemethod;

FIG. 2 shows a schematic illustration of a process picture for anapparatus to realize a preferred embodiment of the inventive method withextension in the air circuitry; and

FIG. 3 shows a schematic illustration of a process picture for anapparatus to put one preferred embodiment of the inventive method withan integrated boiler arrangement into practice.

EMBODIMENTS

The process picture shown in FIG. 1 of an apparatus to put the inventivemethod into practice comprises a drum dryer 1, a removal housing 2, acleaning apparatus 3, heat-exchanger 4, a combustion chamber 5, filter 6as well as a chimney 7. A drying vapor fan 8 is arranged between thedrum dryer 1 and the cleaning apparatus 3, a burner exhaust fan 9 isarranged between filter 6 and chimney 7 and between heat-exchanger 4 andcombustion chamber 5 a regulable partial vapor fan 10 is arranged.

Dryer 1 may be provided with a slow-down zone 11 and a metering device12.

The drum dryer 1 is supplied with bulk goods, as for example with woodenchips and/or wooden fibers. The drying gases, which are supplied to thedrum dryer 1 are heated-up via the heat exchanger 4 and havetemperatures in the range of approximately 250° C. up to approximately600° C. The heating of the drying gases in the heat-exchangers 4 isachieved in cross counter flow by means of exhaust gases from thecombustion chamber 5. The exhaust gases have temperatures in the rangeof approximately 750° C. up to approximately 900° C. Inside of thecombustion chamber 5 temperatures of approximately 750° C. up to 1050°C. are achieved, wherein as fuel for example natural gas, oil and/orwood dust or other waste materials from the production of woodenmaterial boards may be used. The different fuels may be used alone or inany combination with each other.

After the drying goods have passed the drum dryer one slow-down zone 11may be provided for the drying goods and/or a removal housing 2 toremove the dried bulk goods. The drying gases respectively the dryingvapors are driven via the drying vapor fan 8 to one or more cleaningapparatuses 3, preferably cyclone separators. Alternatively oradditionally a drying vapor fan may be arranged between the cleaningdevice 3 and the heat exchanger 4. In the cleaning device 3, fine dustand other particles are separated. The separated material may thanadvantageously be passed to the production. After the drying vapors havepassed the cleaning device 3, they are guided to one or moreheat-exchangers 4. Two parallel operating heat-exchangers are preferred.Inside of the heat-exchanger 4 the drying vapors are heated fromapproximately 110° C. to 130° C. up to 250° C. to approximately 600° C.This is done in a cross counter flow operation by means of the exhaustgases of the burner from the combustion chamber 5. Inside of theheat-exchanger 4 a part of the vapor is separated and led to thecombustion chamber 5 as combustion air and/or cooling air. This part ofthe vapor is driven by the regulable partial vapor fan 10. The exhaustgas of the burner, which serves to heat-up the drying gases inheat-exchanger 4, is guided—after passing through the heat-exchanger4—to a filter 6. This is in particular an electrostatic precipitator,preferably a dry type electrostatic precipitator. The filter 6 ispreferably operated in a suction operation, whereby after the filter 6 afan 9 for the exhaust gas of the burner is provided. The thus cleanedexhaust gas of the burner is released via chimney 7 into theenvironment.

According to the invention, the drying of the wood chips is done in adedicated vapor circuit. Thereby a high vapor content can advantageouslybe achieved and thus a gentle drying can be realized, which has apositive effect to the quality of the drying goods. Further, thereby thepollution and thus the wear of the drying circuit can be kept to aminimum. Also the fire protection can be improved due to the indirectheating of the dryer and the dedicated drying circuit.

The regulation (i.e. control) of the regulable partial vapor fan 10 isdone in a preferred embodiment via the pollution level of the exhaustgases of the burner, as for example by means of the concentration ofnitrogen oxides and/or the concentration values of carbon monoxide.Further, the regulable partial vapor fan may be controlled via a maximuminert gas content in the drying circuit or via the oxygen contend in theexhaust gas of the burner.

In a preferred embodiment, the supply of the drum dryer 1 with bulkgoods is done while controlling the water content in the dryer by meansof the metering device 12, whereby the bulk goods are metered dependingon the moisture of different bulk good fractions upon supply to the drumdryer 1.

Preferably different exhaust gases from the manufacturing of the woodenmaterial boards are used as combustion air for the burner, as forexample exhaust gases from the press arrangements, exhaust gases fromthe sawing arrangements and/or exhaust gases from the boiler. Thedifferent exhaust gases are preferably pre-heated before they aresupplied as combustion air, in particular by means of heat-exchangers.

FIG. 2 shows a process picture of an inventive apparatus for thecontinuously drying of bulk goods, wherein different possibilities ofair flow are shown. The different elements of the apparatus have thesame reference number as in FIG. 1. The drying vapor fan 8 is arrangedbetween the cleaning apparatus 3 and the heat-exchangers 4. Thisarrangement can be provided alternatively or in addition to thearrangement of the drying vapor fan 8 between a dryer 1 and cleaningapparatus 3. The cooling air is led to the burner 5 via two ringsarranged in the ceiling of the combustion chamber. This cooling air isbranched off from the drying vapors inside of heating exchanger 4 anddriven via the regulable partial vapor fan 10. This air flow may besupplemented or replaced by an additional air supply 13. Further, thisair flow may be supplemented by separating a part of the heated dryinggases after the heat-exchanger 4. These switchable air flows are shownby dashed lines in FIG. 2. The exhaust gases of the burner which leavethe burner 5 can be provided before they are passed to theheat-exchangers 4 with additional exhaust gases of the burner, whichalready passed through the heat-exchanger 4, and in particular withexhaust gases of the burner, which already have passed through thefilter 6. These exhaust gases of the burner may alternatively or inaddition be provided as cooling air for the muffle and/or combustion airfor the combustion chamber 5. Fans 14 and 15 are preferably provided todrive these exhaust gases of the burner.

The combustion air for burner 5 can preferably be taken from differentsources. For example, one can use exhaust gases from the press air 16and/or exhaust gas from the sawing arrangements 17. This exhaust gas isdriven via a further fan 18 and provided to the combustion chamber 5 ascombustion air. Preferably, this combustion air is pre-heated before itis passed to the combustion chamber 5, in particular via aheat-exchanger 19, which is heated from boiler exhaust gas 20.Preferably, this boiler exhaust gas is passed after being led throughheat-exchanger 19 to filter 6 and released via chimney 7 to theenvironment.

FIG. 3 shows a further embodiment of an apparatus for the inventivemethod with an integrated boiler arrangement and with different airflows. The different elements of this apparatus are provided with thesame reference numbers as in FIG. 1. The apparatus comprises a dryer 1,a removal housing 2, a cleaning apparatus 3 in form of two cycloneseparators and a heat-exchanger 4 in the actual drying circuit. Theheat-exchanger 4 is supplied with exhaust gases of the burner fromburner 5. Inside of the heat-exchanger 4 a partial flow of the dryingvapors is branched off. This partial flow is driven via the regulablepartial vapor fan 10 and led to the burner 5 as cooling air. The coolingair supply is done via inner and outer nozzle rings 13 being arranged inthe ceiling of the combustion chamber of burner 5.

Muffle 21 of burner 5 is cooled by supply of cooling air. This coolingair is driven via fan 15. The supply of this cooling air respectivelythe cooling of muffle 21 can be achieved by different lines. Forexample, the cooling of the muffle may be done with fresh air 25.Alternatively or in addition to this a supply of a part of vapors 22, asupply with exhaust gas of the burner after heat-exchanger 23, or asupply with an exhaust gas after the electrical precipitator 24, can bearranged. The supply of these different air flows can be done bycorrespondingly provided valves. The combustion air for burner 5 isdriven by fan 18. As combustion air one may use exhaust air from press16 respectively from the saw 17 and/or other kind of exhaust gases 27can be used. These exhaust gases are heated via a heat-exchanger 19 inparticular with an air-to-air heat-exchanger.

The supply as combustion air is controlled via a heating pot 26. Theheat-exchanger 19 is fed with exhaust gases from the boiler, whichresult from the boiler arrangement 28. In order to control thetemperature of the exhaust gases from the boiler being directed toheat-exchanger 19, an additional heat-exchanger 29 may be provided, inparticular a thermo oil heat-exchanger. The pre-heated combustion airmay be guided by a corresponding switching arrangement inside of theheating pot 26 to the burner 5, to the boiler arrangement 28 and/or thechimney 7.

1. Method for continuously drying bulk goods, in particular wood fibersand/or wood chips, in a dryer (1), in particular a drum dryer, which issupplied with bulk goods and through which a vapor gas mixture passes ina drying circuit, wherein the vapor gas mixture is indirectly heated viaat least one heat exchanger (4) by a burner exhaust gas and wherein thedrying vapors are guided and heated up in the at least one heatexchanger (4) and wherein upstream, downstream and/or within the atleast one heat exchanger (4) at least a partial flow of the dryingvapors is branched off to be conducted into the burner (1),characterized in that the partial flow to the burner (5) is driven bymeans of at least one regulable partial vapor fan (10).
 2. Methodaccording to claim 1, characterized in that the partial vapor fan (10)is regulated via the pollution level of the burner exhaust gases, inparticular by nitrogen oxides and/or carbon monoxides.
 3. Methodaccording to claim 1 or 2, characterized in that the partial vapor fan(10) is regulated according to the oxygen content in the exhaust gas ofthe burner.
 4. Method according to anyone of the preceding claims,characterized in that the partial vapor fan (10) is regulated via amaximum inert gas content in the drying circuit.
 5. Method according toanyone of the preceding claims, characterized in that the burner exhaustgas is cleaned by at least one filter (6), in particular anelectrostatic precipitator, preferably a dry type electrostaticprecipitator.
 6. Method according to claim 5, characterized in that thefilter (6) is operated in suction mode, wherein preferably at least oneburner exhaust gas fan (9) is located downstream from the filter. 7.Method according to anyone of the preceding claims, characterized inthat, at least partially, solids are used as fuel for the burner (5), inparticular biomass, wherein preferably waste products from theproduction of the wooden material boards are used.
 8. Method accordingto anyone of the preceding claims, characterized in that the dryingvapors are cleaned after passing through the dryer (1), wherebypreferably as cleaning apparatus (3) at least one cyclone, in particularat least one cyclone battery is used.
 9. Method according to anyone ofthe preceding claims, characterized in that the drying vapors after thedryer (1) are driven by at least one drying vapor fan (8).
 10. Methodaccording to anyone of the preceding claims, characterized in that thewater content in the dryer (1) is regulated, whereby preferably the bulkgoods are metered depending on the moisture of different bulk goodfractions when supplying the dryer (1).
 11. Method according to anyoneof the preceding claims, characterized in that the burner (5) issupplied with at least one further exhaust gas as combustion air and/orcooling air, wherein preferably the additional exhaust gas is taken fromthe manufacturing of the wooden material boards, and is in particularexhaust gas from the presses, exhaust gas from the sawing arrangementsand/or exhaust gas from the boiler.
 12. Method according to claim 11,characterized in that the additional exhaust gas is preheated before itis supplied as combustion air.
 13. Method according to anyone of thepreceding claims, characterized in that the cooling air supply in theburner (5) occurs via an inner and an outer nozzle ring in the ceilingof the combustion chamber, wherein preferably the nozzle rings can beregulated separately from each other.
 14. Method according to claim 13,characterized in that the inner and/or the outer nozzle ring has (have)an entering angle between approximately 0 and approximately 60 degrees,which angle is preferably adjustable depending on the fuel used. 15.Method for the manufacturing of wooden material boards, wherein woodlogs are stripped of bark and are processed in a crushing apparatus towood chips and/or fibers, wherein the wood chips and/or fibers are driedin a drying apparatus, wherein the dried wood chips and/or fibers areprocessed to boards in a pressing arrangement, if necessary by addingbinders and/or further additives, and are preferably cut into size,characterized in that for drying of the wood chips and/or fibers amethod according to anyone of claims 1 to 14 is carried out. 16.Arrangement for drying of bulk goods, in particular of wood fibersand/or wood chips, comprising a dryer (1), in particular a drum dryer,at least one burner (5) and at least one heat exchanger (4), which isprovided to indirectly heat a vapor gas mixture for drying the bulkgoods in the dryer (1), at least one branch line, upstream, downstreamand/or within the at least one heat exchanger (4) to the burner (5) tobranch off a partial flow of the drying vapors, and at least one linefor the remaining partial flow to the dryer (1), characterized in thatin the branch line to the burner (5) at least one regulable partialvapor fan (10) is provided.
 17. Apparatus according to claim 16,characterized in that the partial vapor fan (10) is regulable via thepollution level in the burner exhaust gas, in particular by nitrogenoxide and/or carbon monoxide.
 18. Apparatus according to claim 16 orclaim 17, characterized in that the partial vapor fan (10) is regulatedby the oxygen content in the burner exhaust gas.
 19. Apparatus accordingto anyone of claims 16 to 18, characterized in that the partial vaporfan (10) is regulable by the maximum inert gas content in the dryingcircuit.
 20. Apparatus according to anyone of claims 16 to 19,characterized in that for the cleaning of burner exhaust gases at leastone filter (6) is provided, in particular an electrostatic precipitator,preferably a dry type electrostatic precipitator.
 21. Apparatusaccording to claim 20, characterized in that a burner exhaust gas fan(9) is positioned downstream of the filter (6).
 22. Apparatus accordingto one of claims 16 to 21, characterized in that for cleaning of thedrying vapors a cleaning arrangement (3) is provided, in particular atleast one cyclone, preferably at least one cyclone battery. 23.Apparatus according to one of claims 16 to 22, characterized in thatdown-stream of the dryer (1) at least one drying vapor fan (8) isprovided.
 24. Apparatus according to one of claims 16 to 23,characterized in that to regulate the water content in the dryer (1), ametering device (12) is provided.
 25. Apparatus according to one ofclaims 16 to 24, characterized in that at least one supply line foradditional exhaust gases as combustion air into the burner (5) isprovided.
 26. Apparatus according to claim 25, characterized in that aspreheating devices, in particular heat exchanger, are provided for apreheating of the additional exhaust gases before the same are suppliedto the burner (5).
 27. Apparatus according to anyone of claims 16 to 26,characterized in that the burner (5) comprises a combustion chamberceiling with an inner and an outer nozzle ring being separatelycontrollable.
 28. Apparatus according to claim 27, characterized in thatthe inner and/or outer nozzle ring comprises an entering angle ofapproximately 0 degrees to approximately 60 degrees.
 29. Arrangement forthe manufacturing of wooden material boards with at least one crushingdevice, at least one drying device and at least one pressing device,characterized in that a drying arrangement according to the apparatus ofany of claims 16 to 28 is provided.